The objectives are to quantify and to examine the interactions of receptors on the human red cell membrane with antibodies, lectins and drugs. The methods used for quantitation and topography include radioiodinated and enzyme-labeled antibodies and measurements of hemagglutination in the Auto Analyzer continuous flow system. Endocytosis induced by the action of drugs is used for studying the behavior of membrane surface receptors especially as influenced by changes in metabolic activity and diseases affecting red cell morphology. A later phase of this research will include immunochemical studies of protein fractions from solubilized red cell ghosts. BIBLIOGRAPHIC REFERENCES: Greenwalt, T.J., Jamieson, G.A. (eds.): Transmissible Disease and Blood Transfusion. Grune & Stratton, New York, 1975. Greenwalt, T.J., Steane, E.A.: Theoretical aspects of red cell agglutinability. Abstracts XIVth Congress of the International Society of Blood Transfusion, Helsinki, 1975, p. 120 (abstract).